| Abstract | According to the prescriptive requirements of the 2020 edition of the National Energy Code of Canada for Buildings (NECB), each building envelope component is required to achieve a maximum area-weighted effective thermal transmittance (U_t), which includes the impact of major thermal bridges. This approach differs from how other international standards, such as ASHRAE 90.1-2022, regulate thermal bridging, which may cause confusion for building professionals. Thus, this study aims to provide Canadian building professionals with a practical reference for determining the initial clear-field thermal transmittance (U_o) required to comply with NECB 2020 requirements. Using a simulation-based approach, the study identifies the U_o values necessary for wall assemblies to compensate major thermal bridging. Fourteen distinct commercial building archetypes were analyzed, with simulations conducted across each of the Canadian climate zones. Various façade layouts were examined by altering vertical fenestration and door area to gross wall area ratios (FDWR). Additionally, different thermal bridging design options—categorized as "poor," "regular," and "efficient" performance—were evaluated to understand their impact on the required clear-field transmittance. The findings indicate that in the coldest Canadian climate zones, the majority of buildings will have technical challenges to meet the envelope prescriptive requirements of the NECB as there are no physical and cost-effective solutions to achieve the required clear-field thermal transmittance values to compensate thermal bridging. |
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